The effect of CNS stimulation and psychological stress on the physiology and pathology of the myocardium is studied. Cardiac responses elicited by electrical stimulation of CNS structures involved with the regulation of the autonomic nervous system in rat and cat and by the environmental stress of free operant shock avoidance in the squirrel monkey. Hearts and other organs are removed from these animals at the termination of the experiment and examined for pathological changes. Assessment techniques will include standard histological procedures and biochemical determinations of changes in intracellular calcium and myofibrillar ATPase activity. By careful assessment of these data, the changes in physiological function induced by CNS and environmental stimulation necessary to produce functional disturbances of the myocardium are ascertained. Modifications of these effects by behavioral, pharmacological and surgical techniques are used to analyze the factors which are involved in cardiac dysfunction and pathology. These investigations will contribute not only to the physiology of cardiac function but also help understand CNS mechanisms and psychological factors involved in myocardial necrosis and cardiac dysrhythmias elicited by emotional stress.